The invention relates to improvements in particles (hereinafter called corpuscles) which contain a biologically inert material and medicine distributed in the inert material. Corpuscles of such character are utilized for implantation into animal bodies so that the medicine contained in their biologically inert material can be released into body tissue. By way of example, the inert material can constitute polymethyl methacrylate, and the medicine which is contained in such material can include one or more pharmaceuticals which are or which can be uniformly distributed therein. It is customary to string two or more corpuscles onto a fiament, such as a length of wire or thread, which can facilitate implantation as well as withdrawal of the thus obtained composition from an animal body.
Published German patent application No. 23 20 373 discloses spherical corpuscles. Such corpuscles can contain antibiotics and are widely used for the treatment of infections of bones and/or other parts of bodies. An advantage of such procedure is that the medicine is implanted into immediate proximity of the infected area which greatly reduces the potential undesirable effect of the implanted medicine upon other body parts, such as organs, which are not afflicted and/or should not be influenced by certain types of medicines.
European patent application No. 0 157 909 discloses corpuscles having a spheroidal shape (i.e., they constitute ellipsoids of revolution). This is intended to ensure a more satisfactory surface-to-volume relationship than in the event of the utilization of spherical corpuscles. However, the making of spheroidal corpuscles is more complicated and more expensive. Furthermore, it was ascertained that the clinical application of spheroidal corpuscles does not invariably ensure the required concentration of medicine in the afflicted tisue, namely a concentration which is required to ensure the achievement of satisfactory therapeutical results. Thus, the utilization of such corpuscles does not ensure a sufficient increase of the rate of accurately controlled release of medicine well beyond that which can be achieved by resorting to spherical corpuscles. Furthermore, controlled release of medicine is particularly difficult when the corpuscles must be implanted into certain parts of an animal body.
Attempts to make corpuscles having one or more pointed portions or sections have net with little success, primarily because the making of such corpuscles presents many problem and contributes significantly to their cost.
Another drawback of presently known corpuscles (namely those having a spherical or spheroidal shape) is that they cause the neighboring tissue to fill up or bulge so that they cannot be readily implanted immediately beneath the skin or between the skin and a bone which is closely adjacent the skin. Similar problems arise when spherical or spheroid corpuscles are to be applied to auxiliary osteosynthetic instruments or implements or parts. Furthermore, spherical and/or spheroidal corpuscles cannot be confined in large quantities in bone cavities because too much empty space necessarily remains between the abutting corpuscles of such configuration. This, in turn, exerts an adverse influence upon the quantities of medicine which can be released in the interior of a bone.
The quantities of medicine which can be released by the biologically inert material of a corpuscle depend upon the area of the external surface of the corpuscle. As a rule, the initial stage involves the release of medicine from the zones immediately adjacent the exposed surface of a corpuscle, i.e., the clinically relevant release during the first days following the implantation of a string of corpuscles is not influenced, or is not noticeably influenced, by the medicine which is confined and distributed in the central portion or core of a corpuscle. It can be said that corpuscles having spherical surfaces or surfaces having circular cross-sectional outlines in several planes which are normal to each other and bisect the corpuscles can release only relatively small percentages of medicine which is distributed in their biologically inert material.
Still another problem which is encountered when one utilizes strings of presently known spherical or spheroidal corpuscles is that they cannot be readily withdrawn from the body. The filaments which maintain a file of corpuscles close to each other are used for withdrawal of the corpuscles in response to the exertion of a pull. Such withdrawal is frequently difficult or impossible because the healing process often involves the development of granular tissue which opposes the extraction of spherical or similar corpuscles upon completion of the healing step or when the corpuscles must be removed for other reasons. One of the reasons for such difficulties is that the cross-sectional areas of spherical or spheroid particles are relatively large.